Arterial blood for diagnostic testing the blood gas analyzers is commonly collected by means of syringes, vacuum tubes, or capillary tubes, each of which presents substantial disadvantages and difficulties. Syringes must be airtight and, if formed of glass, usually require lubrication. The entire dead space between the needle and the plunger must be filled with a heparin solution, a procedure requiring considerable care to avoid small air bubbles that may cling to the barrel or to the plunger and prevent anerobic sampling. After collecting the blood, any residual air in the syringe must be expelled to prevent the loss of carbon dioxide from the blood by diffusion.
Although arterial blood can also be collected in heparinized vacuum tubes, the requirement that such tubes be filled completely with blood (to avoid a loss of pCO.sub.2 and an increase in pH) renders such a procedure especially difficult. Also, there has been indications that utilizing a vacuum for drawing blood samples may under some circumstances tend to cause hemolysis.
The use of heparinized capillary tubes has the advantage over the other techniques of avoiding the collection of excessively large samples, a particularly important consideration in pediatric studies, but in order respects the procedures used with such capillary tubes involve the same problems of collecting, transporting, and delivering samples under substantially anerobic conditions.
A main object of this invention therefore lies in providing a device which greatly simplifies the procedures for sampling arterial (and venous) blood, and for doing so in a way that minimizes risks of exposure to air and increases the reproducibility and accuracy of test results. Another object is to provide a relatively safe, uncomplicated, inexpensive, and highly effective device for drawing micro samples of arterial or venous blood and for storing, transporting, and delivering such samples to suitable blood analysis equipment. A still further object is to provide a device which may be used to collect micro samples of different selected volumes depending on the size of the capillary tube releasably joined to the adapter-handle of the assembly.
Briefly, the device includes a capillary tube, an adapter-handle detachably connected to the tube, and a hypodermic needle detachably mounted on the adapter-handle. A protective cover may extend over the needle, and at least one end cap is provided to seal the end (or ends) of the capillary tube after a blood sample is collected.
The adapter-handle is formed of resilient plastic material and has integral body and tip sections. A bore extends longitudinally through both sections with that portion of the bore within the body section tapering gradually inwardly at an angle of approximately 2 to 6 degrees measured from the axis of the adapter-handle. The tip of the adapter-handle has reduced outside cross sectional dimensions and is tapered both internally and externally. The external taper is that of conventional Luer taper, permitting the tip to be inserted and retained within the hub of a standard hypodermic needle having a female Luer taper. The internal taper of the tip extends inwardly at an angle in the range of about 1 to 3 degrees and is dimensioned to receive and sealingly engage the inlet tubes of various models of commercially-available blood gas analyzers. Between the Luer-variable outer surface of the tip and the generally cylindrical outer surface of the body is a more sharply tapered surface of a frusto-conical intermediate section, such surface being adapted to engage and seal against the mouths of the inlet passages of other types of available blood gas analyzers.
In use, the heparin-coated capillary tube, the resilient adapter-handle, and the needle are assembled. A suitable artery or vein is punctured and the capillary tube is filled by reason of arterial or venous pressure. The free end of the capillary tube is then capped, thereby preventing blood from escaping from either end of the capillary tube when the needle is withdrawn from the puncture site. If analysis is to occur immediately, then the user simply mixes the sample with the heparin within the tube, detaches and discards the needle, couples the tip portion of the adapter-handle to a blood analyzer, removes the cap, and allows the micro sample to be drawn into the analyzer. If, on the other hand, any delay is to be encountered before analysis, the user detaches (and discards) the adapter-handle, replaces it with an end cap, and then, following mixing, transit and/or storage, removes both caps, replacing one with a fresh adapter-handle for delivering the sample to the inlet of a blood analyzer in the manner already described.
Other advantages, objects, and features of the invention will become apparent from the drawings and specification.